Pigging device and detection system



y 1968 G. A. FREDERICK ETAL 3,384,512

PIGGING DEVICE AND DETECTION SYSTEM Filed Oct. 21, 1966 2 Sheets-Sheet 1i A MEASURING DEVICE CONTROL CABINET ALCOHOL- STORAGE INVENTOQS GEOQGEA. FDEDEQICK LEONARD E. BURCHARD lam/2W?I m s.

May 21, 1968 G. A. FREDERICK ETAL PIGGING DEVICE AND DETECTION SYSTEMFiled Oct. 21, 1966 2 Sheets-Sheet 2 [LAUNCH ISOLENOID L DELAY 20 secsCOUNTER INVENTOQS GEOQGE A FQEDEDICK LEONARD E. BURCHAQD United StatesPatent ABSTRACT OF THE DISCLOSURE A pigging device launching detectingsystem. Means are provided for launching a pigging device into acarrying 1 line. An electrical sensing means is provided for respondingto the passage of a magnet-containing pigging device past apredetermined point in the pipeline. Control means are operable inresponse to signals from the electrical sensing means and are adapted toregulate the launching means.

This application is a continuation-in-part of application Ser. No.505,625 filed Oct. 29, 1965, now abandoned.

This invention relates to an improved system for controlling the launchand detection of so-called pigging devices in a gathering system such asthat used for conveying natural gas from individual wells or productionareas to collection points. In particular, the invention relates to animproved pigging device detection and control system which is operatedby electrical sensing means to eliminate problems heretofore encounteredusing mechanical means.

By way of background, operation of a large-volume, cross-country,natural gas transmission pipeline involves, at the producing end of thepipeline, the operation of a very extensive gathering system. Thegathering system conveys natural gas from individual wells or individualproduction areas to collection points where the gas is then passed tothe main, long distance-large volume transmission line. The gatheringsystem pipelines are normally smaller in diameter than the main gastransmission line.

The operation of a gathering system is very complex, because manydifferent types of natural gases, including natural gas of varyingliquid condensate content, natural gas of varying sulfur and corrosivecomponent content, and varying amount of moisture are handled. Thegathering systems usually consist of 4- to 12-inch diameter pipe orlarger, and have a great number of valves, fittings and pressureregulators installed to control the fiow of gas from the variousproducing wells. Problems in efficient operation and maintenance ofthese gathering systems are introduced due to liquid condensateaccumulation, fouling due to corrosive components in the natural gas,and the formation of hydrocarbon hydrates. These hydrates, mixtures ofhydrocarbons and water, freeze at temperatures well above normalfreezing points for either the hydrocarbons or water separately andoften completely plug the gathering system pipeline.

It is common practice in the operation of these gathering systems toclean the interior of the pipelines by a process known as pigging. Apipeline pig for this operation usually consists of a hard rubber sphereof substantially the same diameter as the interior of the pipe sectionto be cleaned. The pig is introduced into the pipeline through aseparate connection known as a pig launcher. The pig travels through thesection of pipe which is identical to its diameter and pushes thedeposits described above, ahead of itself, and in the direction of thegas flow. These deposits are then transferred to a larger pipe sectionwhere for example, the 4-inch main joins a 6- or 8-inch section of thegathering system. At this junction another pigging 3,384,512 PatentedMay 21, 1968 sphere is introduced. This additional pig is appropriatelysized for the larger pipe and continues with the cleaning action of thesystem. This larger pig traps and pushes the smaller pig as well as thedeposits collected by the smaller pig.

In a gathering system composed of several different sizes of pipelines,there must be provided pig launchers and pigging spheres sized for eachpipeline diameter.

The cleaning process involves the launching and detection of pigs asthey travel through the pipeline. In addition, it is desirable in somecases to dilute or to clean the hydrate formations by injecting alcoholsuch as methanol or ethanol into the pipeline. Alcohol will dissolve thehydrocarbon hydrates and allow them to be pushed through the pipeline toa point where they can be collected and removed without plugging themain lines.

The use of alcohol for removal of the cleaning operation depends uponknowing the exact location of the pigs in each of the pipe legs of thegathering system. The precise time for launching the next larger pig isdetermined when the smaller pig reaches a junction point or a pipediameter change in the gathering system. In practice, it has been verydifiicult to identify and locate pigs of various sizes and to time thealcohol injections to accomplish the cleaning of the gathering system.

The current practice in locating and timing pipe pigs is to use amechanical contact tripping device to sense the passage of a pig. Thisdevice has an arm or a shaft extending into the pipeline such that thespherical pig traveling in the pipeline makes physical contact withthearm or shaft causing the arm to move. This arm movement is used toactuate external devices to cause another pig to be launched, or torelease an alcohol injection, or to otherwise identify and locate pigsin the system.

However, use of mechanical trip devices has not been satisfactory.Hydrate plugs, slugs of liquid condensates and other deposits inside thepipe cause the mechanical shaft or arm to move and thus give a falseindication that a pigging sphere has passed that point. Also, hydratesmay cause the contact shaft to freeze, preventing the device fromdetecting the passage of any objects. In addition, methods for attachinga timing device to the mechanical shaft to launch additional pigs orcontrol alcohol injection have not been practical or feasible.

In order to solve the problem. in the art of detecting and countingpigging devices, we have developed a unique and novel system forprecisely identifying and counting the devices. Our system also providestiming functions so that alcohol injections can be precisely controlled.Further, a launching signal for pigs following alcohol injection isprovided. This new method of precisely locating, counting, andcontrolling the flow of pigging devices has measurably reduced the costof maintaining gathering systems for natural gas transmission lines andhas inc eased the lifetime and efficiency of operation of the gatheringsystems.

It is therefore an object of our invention to provide a pigging devicelaunch and detection system whereby complete accuracy is attained in thetimed launching of devices and in the detection of launched devices.

It is a further object of our invention to provide such a system whichis free from mechanical failures due to impurities in natural gasgathering system lines.

It is yet another object of this invention to provide such a systemwherein the launching and detection of pigging devices is accomplishedby electrical sensing and control means thus eliminating all need formechanical contact between pigging devices and position sensing means.

It is a further object of this invention to provide a pigging devicelaunching and detection system into which is integrated a system fortime-controlled injection of 3 alcohol into the gas gathering lines,coordinated with the launching of new pigging devices.

It is a further object of this invention to provide a novel piggingdevice which is capable of actuating an electronic control and detectionsystem upon passing. a prede termined point in a gas line.

The above and other objects will become apparent as the invention ismore fully. described hereinafter.

In the drawings:

FIG. 1 is a schematic diagram showing a top view of the pig launcher,and the detection and control systems of the invention;

FIG. 2 is a side view along line 2-2 of FIG. 1;

FIG. 3 is a side view along line 33 of FIG. 1;

FIG. 4 is a circuit diagram showing the system control elements; and

FIG. 5 is a view in section of one embodiment of the novel piggingdevice of the invention.

In the practice of our invention the following principle is utilized: apermanent magnet passing through or by a coil of wire will induce anelectric voltage in the coil which in turn will operate counters andother devices to detect, locate, and time the passage of piggingdevices. To accomplish this, a permanent magnet is positioned in theinterior of each of the rubber pig devices and a coil of wire is wrappedaround or placed on the outside of the pipe at the point where it iswished to detect passage of the devices.

In earlier practice of this basic idea, We had tried to locate the coilon the inside of the pipeline because it was thought that the pipelinesteel itself would conduct all magnetic fields to ground. Surprisingly,however, upon attempting to determine the amount of pickup that could beobtained on the outside or the pipeline, we discovered that there wasenough measurable signal on the exterior surface of the pipeline toallow proper operation of our electronic detector, counter, and launchercontrol mechanisms. This greatly simplified the problem of installing adetector on a high pressure gas gathering system. Since the pick-upsystem is external to the pipeline, there is not need to design specialtransducers or pick-up coils that would be both explosion proof anduseful for detection service at high pressures.

In the operation of this detection device, we insert permanent magnetsin the interior of each of the rubber pigging devices such as the sphereas shown in FIG. 5.

Although the shape and placement of the magnet is not I critical, wehave found that Alnico magnets illustrated at 10 in FIG. 5, ofcylindrical shape, approximately l-inch in height and 1 /2 inches indiameter, are quite suitable for use with a rubber pigging device asillustrated at 15 in the 4-inch to 12-inch diameter sizes. These Alnicomagnets have a field strength of approximately 2000- 3000 gauss. We havefound that the geometry of the magnetic pick-up coil needed fordetection of these spheres 'with our system is independent of the pipediameter, the diameter of device, or magnet embedded in the device.Also, the magnet need not be embedded at the center of the device, asurface or intermediate location being satisfactorily operable.

We have further found that a coil of wire Wrapped circumferentiallyaround the pipe Works equally as well as a loop coil placed horizontallyalongside the pipe wall section. Thus the desired practice in theoperation of this invention is to wrap the coil around the circumferenceof the pipe, although it is within the scope and spirit of our inventionto locate the wire in any configuration whatsoever so long as it picksup a detectable signal from an internally moving device. This practiceof circumferential wrapping greatly increases the mechanical strength ofthe coil, as well as lends stability and ease of installation.

Referring to FIG. 1, our pig launching and detection system comprisebasically three parts: a pneumaticallyoperated pig launcher showngenerally at 1; a control and detection section shown generally at 2including a wire coil 2a wrapped circumferentially around a gas line anda control cabinet containing electrical control elements hereinafterdescribed; and an alcohol injection system shown generally at 3.

Fig launcher 1 consists of a pig storage pipe 4 into which rubber pigshaving in their interior a permanent magnet as above described areloaded from the left as shown in FIG. 1. Pipe 4 is slightly inclined tothe horizontal as shown in MG. 3. Pipe 5, generally horizontallyoriented, houses a pneumatic launcher consisting of an axially slidablepiston (not shown) which reciprocates in pipe 5 upon pneumatic actuationfrom a source of compressed air 9 to force a pig into pipe 6. Thepneumatic launcher is well known in the art and is similar to the onesheretofore used in pig launching systems. As can be seen from FIGS. 2and 3, pipe 6 is oriented at about 45 to the horizontal so that a pigdriven to its upper end will then fall under the combined force ofgravity and pneumatic pressure down into gas line 7 as shownschematically by spherical device 8. Once into gas line 7, the pig isthen forced by the fiow of gas in the gas line toward coil 2a and ondownstream.

Alcohol injection system 3 consists of a storage tank It generallyhorizontally oriented, connected by a suitable valve or orifice to ameasuring device 11. Device 11 in turn is connected to gas line 7 bymeans of control valve 2 which is opened and closed in response toelectrical signal from the control cabinet, hereinafter more fullydescribed. Measuring device 11 is basically a calibrated cylindricalcontainer which holds an amount of alcohol desired for a singleinjection into line 7. After emptying through valve 12 in response fromthe control cabinet, the measuring device is refilled from storage tankIt in preparation for the next injection.

The operation of the electronic amplifying and control circuit andsignal detection device is briefly explained as follows: A piggingdevice containing a magnet and coming from upstream in the gas linemoves through coil 2a wrapped around pipeline 7 as shown in FIG. 1 andproduces a small voltage due to this movement. This electrical voltageor pulse is the input to electronic circuitry which performs thefollowing action: (1) The signal is first amplified and then is directedby gating circuitry, namely a counter (not shown) that determines ifthis is a device upon which a larger device is to be launched. (2)

If it is determined to launch a device, alcohol is then injected intothe pipeline for a pre-determined interval of time. The duration of thealcohol injection period is controlled by a thermal delay-relay. (3) Thelaunched device enters the pipeline upstream of coil 2a, thusnecessitating the newly-launched device to pass through it. Circuitrythat had been preset by the initial device passing through the coildirects the second induced pulse from the coil to a counter whichindicates the successful launchof a new device. (4) Two electronicmechanical counters are provided, one to show the accumulation ofdetected devices and the other to show the accumulation of launcheddevices.

FIG. 4 shows the circuitry used in our invention. Both relay and solidstate circuits have been utilized and found to be reliable inoperation.FIG. 4 is a relay circuit, but it should be understood that such circuitcan be fully transistorized to provide a reliable and compact controlsystem.

In FIG. 4, coil 2a is connected to amplifier 13 and then through anelectronic counter which includes a high impedance matching device 14,well-known in the art, to a first coil 15 and, through contacts 49 to asecond coil 16. Coils 15 and 16 are powered by battery 17 or othersource of direct current. Coil 15 controls contacts 40 which close uponenergizing coil 15. Coil 16, when energized upon closing contacts 40,closes contacts 26 which completes a circuit through coil 18 to battery19 through normally-closed contacts 38, and also completes a circuitthrough coil 27 to battery 28. Coil 18, powered by battery 19, controlsfour sets of contacts 20a, 20b, 20c and 20d. Contacts 201: complete acircuit from battery 19 through coil 18 to one contact of a thermal timedelay 21 to terminal is connected to contacts 26 which are open socounter 37 does not register.

For the duration that time delay 30 is closed seconds after time delay21 opens), counter 37 is activated ground. Contacts b complete a circuitbetween battery 5 and will record an event when the newly launched pig22 and the coil of thermal time delay 21 to ground. Conpasses throughcoil 2a and causes contacts 26 to close. tacts 20c, normally closed,complete a circuit between Such event will not energize relay 18 tostart a new cycle battery 22 and first counter 23 and pig launchsolenoid since contacts 38 are open. At the end of 20 seconds, 24, whencontacts are closed. Counter 23 and solenoid time delay breaks thecircuit energizing coil 27, con- 24 are in parallel and operateindependently of one an- 10 tacts 25 open and counter 37 is deactivated.The system other. Contacts 200 also complete a circuit between batisthen ready for a new sequence of events. tery 22 and coil 39 to ground,when contacts 25 are The following table shows a three-day operationusing closed. Contacts 20d complete a circuit between battery amechanical pig detection system of the prior art and 22 and alcoholinjection solenoid 25a. the electrical systems of our invention. Theresults il- Contacts 29 complete a circuit between battery 28 and 15lustrate that the mechanical system is not reliable for one contact oftime delay 30 to ground. Contacts 31 comcounting detected pigs while oursystem operated withplete a circuit from battery 32 through the coil ofthermal out errors,

TABLE 1 Counter Reading Time Mechanical Electrical Remarks Launched Detected Launch ed D etected First day:

2:00 m 0000 0000 0003 0003 Initial. 2:40 p.111 0001 0002 0004 0004 Thetime duration is increased by 3:35 p.1n- 0002 0004 0005 0005 highertemp. 3:20 p.m 0003 000s 0003 0000 7:15 p.rn 0004 0007 0007 0007 Nooscillation or no faulty indication 8:30 p.m 0005 0008 0008 0008 duringnight. Second day 8:30 a. 0000 0000 0000 0000 Reset the counters. 10:000001 0002 0001 0001 10:4 0002 0004 0002 0002 11: 0003 0005 0003 0003 1:0004 0003 0004 0004: 2: 0005 0003 0005 0005 4: 0000 0000 0000 0000 Resetthe counters.

No oscillation or no faulty indication during night. Thlrd day:

8:15 3.111 0001 0001 0001 0001 9:15 3.111.- 0002 0003 0002 0002 Temp.,80 F. 10:15 am. 0003 0005 0003 0003 Temp., 03 F. 12:20 p.m 0005 00030001 0001 Temp.,79 F. 1.30 p.m 0000 0010 0002 0002 3:00 p.m 0002 00020002 0002 Initial. Fourth day:

time delay 30 to ground. Contacts 33 complete a circuit between battery19 through coil 34 to ground through contacts 26, when closed. Contacts35 complete a circuit between battery 36 and second counter 37 toground.

The operation of the above described circuit will now be described. Whena magnet-containing pigging device passes through coil 2a from upstreamin a gasline, a pulse is generated, and a counter device determineswhether this is a pig which is to signal the launch of a new pi-g. Ifso, the pulse generated in the coil is amplified and energizes coil 15to close contacts 40. In turn, coil 16 is energized through the closedcircuit comprising battery 17, closed contacts 40, coil 16 and ground.Contacts 26 are then closed which energizes both coils 18 and 27.

Coil 27 closes contacts 29 and 31 to start time delay 30 which holdscontacts 25 closed for 20 seconds. Coil 18 closes contacts 20a and 20bstarting time delay 21 which holds closed the circuit through contacts20a for 5 seconds. Contacts 200, normally closed, are open during the 5second delay so that counter 23 and launch solenoid 24 are not energizedby battery 22.

During the 5 second delay when coil 18 is energized, contacts 20d areheld closed and the alcohol solenoid is energized and alcohol isinjected into the pipeline. At the end of 5 seconds, time delay 21breaks the circuit through contacts 20a which de-energizes coil 18,opens contacts 20d so that alcohol injection stops, and permits contacts200 to close. Contacts 25 remain closed, of course, since time delay 30is still activated. With contacts 20c closed, the circuit from battery22 to counter 23 and launcher solenoid 24 is closed so that a new pig islaunched and the detected pig is counted. At the same time, coil 39 isenergized and contacts 33 are closed providing potential to one terminalof coil 34. The other From the description of the operation of thisinvention it can be seen that the system is extremely versatile. Thedetector can detect the passage of pigging devices with percentreliability, and it is able to precisely control the launching andalcohol injection processes which are necessary to the efiicientcleaning and maintenance of natural gas gathering systems. It can bereadily seen that our system is extremely sensitive and can be adaptedto centralized control at a distribution headquarters. The informationfrom our detection and launching control system can be telemetered toany desired location Within the gathering system for use withcomputerized techniques for total system control. Cleaning of the entiredistribution and gathering system from one central location is but oneof the many advantages attainable with our system.

Those skilled in the art will recognize that certain modifications canbe made in our invention without departing from the scope thereof.Although reference herein is made to a pigging device in the form of asphere, any form of device may be used, so long as the device presents across section corresponding to that of the fluid transmission line in atleast one part of the device, in the present case, a circular crosssection. Forms other than spheres, such as but not limited tocylindrical, dumbbell, conical, or disc shapes may be usedsatisfactorily. The pig of this invention is also not restricted tobeing formed of hard rubber, and foamed, thermosetting or thermoplasticplastics, metal, glass, and composite bodies or other compositions maybe used. It will also be apparent that the nature of the pipeline isirrelevant to our invention, the system working equally well with, forexample, lines of metals other than steel or iron, glass, or plastics.

It is also intended that the scope of this invention in the devices andoperation of the system here disclosed is not restricted to theheretofore known sole utility of scavenging gathering lines, but isapplicable to all fluid and vacuum transport systems wherein detectionof devices used for cleaning, indicating, counting, separation of twodiflerent fluids therein, or transporting is involved. Thus, the termpigging heretofore having a restricted meaning in the gas and petroleumart, is herein used in the above sense and is thereby redefined to covermore than merely scavenging. For example, the pigging devices describedherein can be used in other fluid-carrying lines for cleaning purposesor to signal the passage of a fluid interface, e.g. in the transportingof diflerent fluids in a petroleum line. In this embodiment theinjection of the pigging devices may be so timed as to coincide with thechange from one liquid to another in the line so that a device closelyprecedes or follows an interface, or acts as a separator.

Also within the scope of this invention is use of the disclosed systemin conjunction with conventional pneumatic, air-veyoring, and vacuumsystems. In the pneumatic or air-veyoring systems, the pig in additionto being used as a separator may also be used, in hollow form withappropriate placement of the magnet, as a carrier receptacle ortransport pig. In this latter form, the pig and the detector system ofthe present invention is useful in conventional vacuum systems for thelocation and counting of transport pigs.

In a fluid-carrying system, the fluids may be gas, including air,liquid, or fluidized solids, or mixtures of the three, transported inany sequence. Thus, a gas may be transported between two liquids, withpigs acting as separators. Normally, the interface will follow the pig,depending of course on differential pressure in the system and densityof the pig, so that the passage of the pig signals a change of fluid tofollow, allowing sufficient time for tap-off devices to be actuated. Itis to be understood that fluidized solids includes slurries, for examplecoal slurries, and solids entrained in a gas, including air.

In short, the novel devices and method of detection described herein canbe used in any vacuum or fluidcarrying system wherein it is desirable tolocate posi tions of materials within the system.

We claim:

1. A pigging device launch and detection system comprising means orlaunching a pigging device into a carrying line, electrical sensingmeans responsive to the pas sage of a magnet-containing pigging devicepast a predetermined peint on said line, and control means operable inresponse to signals from said electrical sensing means and adapted toregulate said launch means.

2. The system of claim 1 wherein said electrical sensing means is a Wirecoil in communication with said line.

3. The system of claim 2 wherein said coil is circumferentially disposedaround said line.

4. The system of claim 3 wherein said device is a sphere, and saidcarrying line is a fluid-carrying line.

5. A pigging device launch and detection system comprising means forlaunching a pigging device into a fluidcarrying line, electrical sensingmeans for detecting passage of a magnet-containing pigging device past apredetermined point on said line, alcohol injection means for injectinga predetermined quantity of alcohol into said line at predeterminedtimes, and control means operable in response to signals from saidelectrical sensing means and capable of regulating said launch means.

6. The system of claim 5 wherein said electrical sensing means is a wirecoil in communication with said line.

7. The system of claim 6 wherein said coil is circumferentially disposedaround said line.

8. Method of cleaning a gas line and of launching and detecting piggingdevices in a gas line having an electrical sensing means responsive tothe passage of a magnetcontaining pigging device, alcohol injectionmeans and a pigging device launch means comprising (1) electricallysensing the pass-age of a first magnet-containing pigging device pastsaid sensing means to provide a first signal (2) injecting alcohol intosaid line downstream of said launching means in response to said signal(3) launching a second magnet-containing pigging device into said gas.line in response to said signal upstream of said sensing means andalcohol injection means, and (4) electrically sensing the passage ofsaid second pigging device past said sensing means to provide a secondsignal.

9. Method of claim 8 wherein said first and second signals actuateelectrical counter means for cumulatively recording passage of piggingdevices past said sensing means.

10. A system for detecting the passage of a pigging device in a carryingline, said system comprising a pigging device having a permanent magnettherein, electrical sensing means positioned at a predetermined positionexterior of and proximate to said line, said electrical sensing meansbeing responsive to the passage of said permanent magnet in said piggingdevice past said predetermined position, and means spaced from saidsensing.

means and responsive to said sensing means for recording that saidpigging device has passed said predetermined position in said carryingline.

11. The system of claim 10 wherein said electrical sensing meanscomprises a wire coil in proximate communication with said carryingline.

12. The system of claim 11 wherein said coil is circumferentiallydisposed around said line.

13. The system of claim 10 wherein said carrying line is a natural gaspipeline, first and second pigging devices having permanent magnetstherein are spaced from each other in said pipeline, and natural gas isinterposed in said pipeline between said first and second pigging devices.

References Cited UNITED STATES PATENTS 2,601,248 6/1952 Brenholdt15.104.06 X 2,953,157 9/1960 Osborne et al. 15-40406 X 3,011,197 12/1961Nehse et al. 15104.06 3,092,991 6/1963 Thompson 733 3,120,118 2/1964Boyle 73-3 3,148,689 9/1964 Bean et al 15-104.06 X 3,232,090 2/1966Walker 15104.06 X

CHARLES A. WILLMUTH, Primary Examiner. EDWARD L. ROBERTS, AssistantExaminer.

